Reconcile "test/utils.py" implementations

Before we move this code to a more suitable place, start by agreeing with small differences in the implementation.

This takes all the nice changes from caddy-frontend/tests/ but not what was specific to caddy or to testing slave instances.

/reviewed-on nexedi/slapos!389

software/erp5testnode/testsuite/caddy-frontend/buildout.hash.cfg

@@ -15,4 +15,4 @@
 
 [template]
 filename = instance.cfg
-md5sum = 2eba374ea5b7ec6c95a1f79066cfb46b
+md5sum = a345d46655c3e841c2ecf4e3a0446c8f

software/erp5testnode/testsuite/caddy-frontend/instance.cfg

@@ -36,10 +36,9 @@ command-line =
   --source_code_path_list=$${slapos:location}/software/caddy-frontend/test
 
 # XXX slapos.cookbook:wrapper does not allow extending env, so we add some default $PATH entries ( not sure they are needed )
-#  PATH=${buildout:bin-directory}:/usr/bin/:/bin/
 environment =
+  PATH=${curl:location}/bin/:${openssl:location}/bin/:/usr/bin/:/bin
   LOCAL_IPV4=$${slap-configuration:ipv4-random}
   GLOBAL_IPV6=$${slap-configuration:ipv6-random}
-  CURL=${curl:location}/bin/curl
   SLAPOS_TEST_WORKING_DIR=$${create-directory:working-dir}
   TEST_SR=${template:test_software_release}